Surfaces previously-computed-but-unused stats into the Claude prompt:
1. USER_PROMPT_TEMPLATE gains a new '### Sim Insights' section that shows:
- Deck-level opening hand quality: avg keptInOpeningHandRate across all
cards, plus the 3 worst offenders with their actual rates
- Curve velocity: avg avgTurnCast weighted by castRate, flagging cards
cast on avg turn > 6 as 'late'
- Synergy outliers: bottom-3 synergyScore cards flagged as 'isolated'
- Archetype weak spots: archetypes with winRate < 40% flagged explicitly
2. _format_archetypes() now annotates weak spots with [WEAK SPOT] and
strong matchups with [STRENGTH] so Claude sees them immediately.
3. _format_top_cards() adds keptInOpeningHandRate to each line so
the 'good' cards also show their hand-keepability signal.
4. New helper _format_sim_insights() computes all deck-level aggregates
from CardPerformance list — no new fields on DeckMeta needed.
No schema changes. Fully backward-compatible with existing DeckReport.